Apparatus for and method of protecting wireless-coupled power devices from overvoltage, overcurrent, and overtemperature using hysteresis

ABSTRACT

An overvoltage protecting unit and an overcurrent protecting unit protect a power device from an overvoltage and an overcurrent using a comparator having hysteresis. An overtemperature protecting unit protects the power device from an overtemperature using a thermistor having a resistance that changes as a temperature of the thermistor changes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 USC 119(a) of Korean PatentApplication No. 10-2011-0046277 filed on May 17, 2011, in the KoreanIntellectual Property Office and Korean Patent Application No.10-2011-0049244 filed on May 24, 2011, in the Korean IntellectualProperty Office, the entire disclosures of which are incorporated hereinby reference for all purposes.

BACKGROUND

1. Field

The following description relates to an apparatus for and a method ofwireless power transmission, and more specifically to an apparatus and amethod that protect wireless-coupled power devices from an overvoltage,an overcurrent, and an overtemperature using hysteresis.

2. Description of Related Art

Wireless power is energy transferred from a wireless power transmitterto a wireless power receiver via magnetic coupling.

Wireless power transmission is a technology for operating a deviceirrespective of a position of the device by wirelessly transferring apower to the device without a wire.

A wireless power receiver may charge a battery using energy receivedwirelessly. A wireless power transmission and charging system includes asource device and a target device. The source device wirelesslytransmits power. The target device wirelessly receives power. The sourcedevice may be referred to as a wireless power transmitter, and thetarget device may be referred to as a wireless power receiver.

The source device includes a source resonator, and the target deviceincludes a target resonator. Magnetic coupling or resonance coupling isestablished between the source resonator and the target resonator. Thesource device and the target device may communicate with each other.During communication, transmission or reception of control informationand state information may occur.

Due to a rapid increase in various electronic devices such as electricvehicles, mobile devices, and other devices that may move or be movedfrom place to place, research on wireless power transmission has beenconducted to overcome problems such as an increase in an inconvenienceof a wired power supply, or a limit of an existing battery capacity. Onewireless power transmission technology uses resonance characteristics ofradio frequency (RF) elements. For example, a wireless powertransmission system using resonance characteristics includes a sourcedevice configured to supply power, and a target device configured toreceive supplied power. To efficiently transmit power from the sourcedevice to the target device, the source device and the target deviceneed to exchange information about a state of the source device andinformation about a state of the target device with each other. In otherwords, there is a need to perform communication between the sourcedevice and the target device.

SUMMARY

According to an aspect, an overvoltage protector includes a firstresistive divider configured to divide an input voltage to produce afirst divided voltage; a rectifier configured to rectify the firstdivided voltage to produce a rectified voltage; a second resistivedivider configured to divide the rectified voltage to produce a seconddivided voltage; and a comparator configured to receive the seconddivided voltage as an input through a positive (+) terminal of thecomparator; receive a direct current (DC) voltage as an input through anegative (−) terminal of the comparator; output a control signal; changethe control signal output by the comparator to a first control signalwhen a difference between the second divided voltage input through the +terminal and the DC voltage input through the − terminal is greater thanor equal to an ON level; and change the control signal output by thecomparator to a second control signal when the difference between thesecond divided voltage input through the + terminal and the DC voltageinput through the − terminal is less than or equal to an OFF level.

The first resistive divider may include a first resistor connected to aninput of the first resistive divider that receives the input voltage,and an input of the rectifier; and a second resistor connected to thefirst resistor at the connection to the input of the rectifier, and aground; and the second resistive divider may include a third resistorconnected to an output of the rectifier, and the + terminal of thecomparator; and a fourth resistor connected to the third resistor at theconnection to the + terminal of the comparator, and the ground.

The rectifier may include a diode including an anode connected to thefirst resistive divider; and a cathode connected to the second resistivedivider; and a capacitor connected to the cathode and a ground.

The first resistive divider may be connected to a drain or a collectorof a power device protected by the overvoltage protector.

The overvoltage protector may further include a control unit configuredto block a signal from being input to the power device when the controlsignal output by the comparator is the first control signal.

The OFF level may be less than the ON level to provide the comparatorwith a hysteresis characteristic.

According to an aspect, an overcurrent protector includes a resistivedivider configured to divide a first input voltage to produce a dividedvoltage; an amplifier configured to amplify the divided voltage toproduce an amplified voltage; a switch configured to connect anddisconnect the resistive divider and the amplifier from each other inresponse to a switch control signal; a first comparator configured toreceive a second input voltage as an input through a positive (+)terminal of the first comparator; receive a first direct current (DC)voltage as an input through a negative (−) terminal; output the switchcontrol signal; change the switch control signal output by the firstcomparator to a signal to turn the switch ON when a difference betweenthe second input voltage input through the + terminal and the first DCvoltage input through the − terminal is greater than or equal to a firstON level; and change the switch control signal output by the firstcomparator to a signal to turn the switch OFF when the differencebetween the second input voltage input through the + terminal and thefirst DC voltage input through the − terminal is less than or equal to afirst OFF level; and a second comparator configured to receive theamplified voltage as an input through a positive (+) terminal of thesecond comparator; receive a second DC voltage as an input through anegative (−) terminal of the second comparator; output a control signal;change the control signal output by the second comparator to a firstcontrol signal when a difference between the amplified voltage inputthrough the + terminal and the second DC voltage input through the −terminal is greater than or equal to a second ON level; and change thecontrol signal output by the second comparator to a second controlsignal when the difference between the amplified voltage input throughthe + terminal and the second DC voltage input through the − terminal isless than or equal to a second OFF level.

The resistive divider may include a first resistor connected to an inputof the switch, and a ground; and a second resistor connected to an inputof the first resistive divider that receives the first input voltage,and the first resistor at the connection to the input of the switch.

The resistive divider may be connected to a drain or a collector of apower device protected by the overcurrent protector.

The overcurrent protector may further include a control unit configuredto block a signal from being input to the power device when the controlsignal is the first control signal.

The first OFF level may be less than the first ON level to provide thefirst comparator with a hysteresis characteristic; and the second OFFlevel may be less than the second ON level to provide the secondcomparator with a hysteresis characteristic.

According to an aspect, an overtemperature protector includes aregulator including an input voltage (V_(in)) input, a reference voltage(V_(ref)) input, and an output; a first inductor connected to a drain ora collector of a power device protected by the overtemperatureprotector, and the V_(in) input of the regulator; a thermistor connectedto a ground, and the V_(ref) input of the regulator, the thermistorhaving a resistance that decreases when a temperature of the thermistorincreases; and a second inductor connected to the output of theregulator, and a gate or a base of the power device.

The regulator may be a low-dropout (LDO) regulator.

The regulator may be a switching-mode regulator.

According to an aspect, an overvoltage protection method includesdividing an input voltage to produce a first divided voltage; rectifyingthe first divided voltage to produce a rectified voltage; dividing therectified voltage to produce a second divided voltage; comparing thesecond divided voltage with a direct current (DC) voltage; outputting acontrol signal based on a result of the comparing; changing the controlsignal to a first control signal when a difference between the seconddivided voltage and the DC voltage is greater than or equal to an ONlevel; and changing the control signal to a second control signal whenthe difference between the second divided voltage and the DC voltage isless than or equal to an OFF level.

The input voltage may be a voltage of a drain or a collector of a powerdevice protected by the overvoltage protection method; and theovervoltage protection method may further include blocking a signal frombeing input to the power device when the control signal is the firstcontrol signal; and allowing the signal to be input to the power devicewhen the control signal is the second control signal.

According to an aspect, an overcurrent protection method includesdividing a first input voltage to produce a divided voltage; comparing asecond input voltage with a first direct current (DC) voltage;outputting a switch control signal based on a result of the comparingthe second input voltage with the first DC voltage; changing the switchcontrol signal to a signal to turn a switch ON when a difference betweenthe second input voltage and the first DC voltage is greater than orequal to a first ON level; changing the switch control signal to asignal to turn the switch OFF when the difference between the secondinput voltage and the first DC voltage is less than or equal to a firstOFF level; turning the switch ON and OFF to supply and not supply thedivided voltage to an amplifier in response to the switch control signalso that the amplifier amplifies the divided voltage and outputs anamplified voltage when the switch is turned ON; comparing the amplifiedvoltage with a second DC voltage; outputting a control signal based on aresult of the comparing the amplified voltage with the second DCvoltage; changing the control signal to a first control signal when adifference between the amplified voltage is greater than or equal to asecond ON level; and changing the control signal to a second controlsignal when the difference between the amplified voltage the second DCvoltage is less than or equal to a second OFF level.

The input voltage may be a voltage of a drain or a collector of a powerdevice protected by the overcurrent protection method; and theovercurrent protection method may further include blocking a signal frombeing input to the power device when the control signal is the firstcontrol signal; and allowing the signal to be input to the power devicewhen the control signal is the second control signal.

According to an aspect, an overtemperature protection method includesapplying a voltage of a drain or a collector of a power device protectedby the overtemperature method to an input voltage (Vin) input of aregulator; applying a voltage determined by a resistance of a thermistorto a reference voltage (Vref) input of the regulator, the resistance ofthe thermistor changing as a temperature of thermistor changes; andapplying an output voltage of the regulator to a gate or a base of thepower device, the output voltage of the regulator depending on Vin andVref of the regulator.

The regulator may a low-dropout (LDO) regulator or a switching-moderegulator.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a wireless power transmission system.

FIG. 2 illustrates an example of a wireless power transmitter.

FIG. 3 illustrates an example of a wireless power transmitter.

FIGS. 4 through 8 illustrate examples of resonators.

FIG. 9 illustrates an example of an equivalent circuit of a resonator ofFIG. 3.

FIG. 10 illustrates an example of an apparatus including anovertemperature, overvoltage, and overcurrent protection scheme.

FIG. 11 illustrates an example of an overvoltage protecting unit.

FIGS. 12A and 12B illustrate an example of an operation of a comparatorhaving hysteresis.

FIG. 13 illustrates an example of an overcurrent protecting unit.

FIG. 14 illustrates an example of an overtemperature protecting unit.

FIG. 15 illustrates an example of an overvoltage protection method.

FIG. 16 illustrates an example of an overcurrent protection method.

FIG. 17 illustrates an example of an overtemperature protection method.

FIG. 18 illustrates an example of an electric vehicle charging system.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. However, various changes,modifications, and equivalents of the methods, apparatuses, and/orsystems described herein will be apparent to one of ordinary skill inthe art. The sequence of processing steps and/or operations describedherein are merely examples, and the sequence of processing steps and/oroperations are not limited to the examples set forth herein, but may bechanged as will be apparent to one of ordinary skill in the art, withthe exception of processing steps and/or operations necessarilyoccurring in a certain order. Also, description of well-known functionsand constructions may be omitted for increased clarity and conciseness.

Throughout the drawings and the detailed description, the same referencenumerals refer to the same elements. The relative size and depiction ofthese elements may be exaggerated for clarity, illustration, andconvenience.

FIG. 1 illustrates an example of a wireless power transmission system.Referring to FIG. 1, the wireless power transmission system includes asource device 110, and a target device 120.

The source device 110 includes an alternating current-to-direct current(AC/DC) converter 111, a power detector 113, a power converter 114, acontrol/communication unit 115, and a source resonator 116.

The target device 120 includes a target resonator 121, a rectificationunit 122, a DC-to-DC (DC/DC) converter 123, a switch unit 124, acharging unit 125, and a control/communication unit 126.

The AC/DC converter 111 rectifies an AC voltage having a frequency oftens of hertz (Hz) output from a power supply 112 to generate a DCvoltage. The AC/DC converter 111 may output a DC voltage having apredetermined level, or may output an adjustable DC voltage having anadjustable level controlled by the control/communication unit 115.

The power detector 113 detects an output current and an output voltageof the AC/DC converter 111, and outputs information about the detectedcurrent and the detected voltage to the control/communication unit 115.In addition, the power detector 113 detects an input current and aninput voltage of the power converter 114.

The power converter 114 may use a switching pulse signal having afrequency of a few megahertz (MHz) to tens of MHz to convert a DCvoltage to an AC voltage to generate a power.

For example, the power converter 114 may use a resonance frequency toconvert a DC voltage to an AC voltage, and the power converter 114 maygenerate a communication power used for communication, or a chargingpower used for charging. The communication power and the charging powerare used in the target device 120. The communication power is a powerused to activate a communication module and a processor of the targetdevice 120. Accordingly, the communication power may be referred to as awake-up power. Additionally, the communication power may be transmittedas a continuous wave (CW) for a predetermined period of time. Thecharging power is a power used to charge a battery connected to thetarget device 120 or a battery included in the target device 120. Thecharging power may be transmitted at a higher power level than thecommunication power for a predetermined period of time. For example, thecommunication power may have a power level of 0.1 Watt (W) to 1 W, andthe charging power may have a power level of 1 W to 20 W.

The control/communication unit 115 may control a frequency of aswitching pulse signal. The frequency of the switching pulse signal maybe determined by the control/communication unit 115. Thecontrol/communication unit 115 may control the power converter 114 togenerate a modulation signal to be transmitted to the target device 120.In other words, the control/communication unit 115 may use in-bandcommunication to transmit various messages to the target device 120.Additionally, the control/communication unit 115 may detect a reflectedwave, and the control/communication unit 115 may demodulate a signalreceived from the target device 120 via an envelope of the detectedreflected wave.

The control/communication unit 115 may use various schemes to generate amodulation signal for in-band communication. The control/communicationunit 115 may turn a switching pulse signal on and off, or may performdelta-sigma modulation, to generate a modulation signal. Additionally,the control/communication unit 115 may generate a pulse-width modulation(PWM) signal having a predetermined envelope.

The control/communication unit 115 may perform out-band communicationthat employs a separate communication channel instead of a resonancefrequency used to transmit wireless power. The control/communicationunit 115 may include a communication module. The communication modulemay be a ZigBee module, a Bluetooth module, or any other type ofcommunication module that is known to one of ordinary skill in the art.The control/communication unit 115 may transmit data to the targetdevice 120 using the out-band communication and/or receive data from thetarget device 120 using the out-band communication.

The source resonator 116 transfers electromagnetic energy to the targetresonator 121. For example, the source resonator 116 may transfer acommunication power used for communication to the target device 120 or acharging power used for charging to the target device 120 using amagnetic coupling with the target resonator 121.

The target resonator 121 receives the electromagnetic energy from thesource resonator 116. For example, the target resonator 121 may receivethe communication power or the charging power from the source device 110using the magnetic coupling with the source resonator 116. As anotherexample, the target resonator 121 may use the in-band communication toreceive various messages from the source device 110 using the magneticcoupling with the source resonator 116.

The rectification unit 122 rectifies an AC voltage to generate a DCvoltage. In this example, the AC voltage is received from the targetresonator 121.

The DC/DC converter 123 adjusts a level of the DC voltage output fromthe rectification unit 122 based on a voltage rating of the chargingunit 125. For example, the DC/DC converter 123 may the level of the DCvoltage output from the rectification unit 122 to 3 volt (V) to 10 V.

The switch unit 124 is turned on or off under the control of thecontrol/communication unit 126. In response to the switch unit 124 beingturned off, the magnetic coupling between the source resonator 116 andthe target resonator 121 may be substantially reduced, causing thecontrol/communication unit 115 of the source device 110 to detect areflected wave.

The charging unit 125 may include a battery. The charging unit 125 mayuse a DC voltage output from the DC/DC converter 123 to charge thebattery.

The control/communication unit 126 may use a resonance frequency toperform in-band communication for transmitting or receiving data. Duringthe in-band communication, the control/communication unit 126 may detecta signal between the target resonator 121 and the rectification unit122, or detect an output signal of the rectification unit 122, anddemodulate a received signal from the detected signal. In other words,the control/communication unit 126 may demodulate a message receivedusing the in-band communication.

The control/communication unit 126 may adjust an impedance of the targetresonator 121 to modulate a signal to be transmitted to the sourcedevice 110. As an example, the control/communication unit 126 may turnthe switch unit 124 on and off to modulate the signal to be transmittedto the source device 110. For example, the control/communication unit126 may increase the impedance of the target resonator 121. Due to theincrease of the impedance of the target resonator 121, a reflected wavemay be detected by the control/communication unit 115 of the sourcedevice 110. In this example, depending on whether the reflected wave isdetected, the control/communication unit 115 may detect a binary number“0” or “1.”

The control/communication unit 126 may also perform out-bandcommunication that employs a communication channel. Thecontrol/communication unit 126 may include a communication module (notillustrated) to perform the out-band communication. The communicationmodule may be a ZigBee module, a Bluetooth module, or any other type ofcommunication module that is known to one of ordinary skill in the art.The control/communication unit 126 may transmit data to the sourcedevice 110 using the out-band communication or receive data from thesource device 110 using the out-band communication.

FIG. 2 illustrates an example of a wireless power transmitter. Referringto FIG. 2, the wireless power transmitter includes a source resonator210, a sub-resonator 220, and a magnetic field distribution controller230.

The source resonator 210 forms a magnetic coupling with a targetresonator. The source resonator 210 wirelessly transmits power to atarget device through the magnetic coupling. The source resonator 210may have a loop shape as illustrated in FIG. 2. However, the sourceresonator 210 may have a shape other than a loop shape, such as a spiralshape, a helical shape, or any suitable shape that is known to one ofordinary skill in the art.

Additionally, the wireless power transmitter may include a matcher (notillustrated) to be used for impedance matching. The matcher may adjust astrength of a magnetic field of the source resonator 210 to anappropriate level. An impedance of the source resonator 210 may bedetermined by the matcher. The matcher may have the same shape as thesource resonator 210. Additionally, the matcher may have a predeterminedlocation relative to a capacitor located in the source resonator 210 toadjust the strength of the magnetic field. For example, the matcher maybe electrically connected to the source resonator 210 at both ends ofthe capacitor.

As an example, the matcher may be located within a loop of the loopstructure of the source resonator 210. The matcher may change thephysical shape of the matcher to adjust the impedance of the sourceresonator 210.

The sub-resonator 220 is located within the source resonator 210. Aplurality of sub-resonators may be located within the source resonator210. Additionally, a sub-sub-resonator may be located within thesub-resonator 220. The sub-resonator 220 may influence a distribution ofa magnetic field formed within the source resonator 210. For example, acurrent flowing in the source resonator 210 may form a magnetic field,and the formed magnetic field may induce a current in the sub-resonator220. In this example, a distribution of the magnetic field formed withinthe source resonator 210 may be determined based on a direction of thecurrents flowing in the source resonator 210 and the sub-resonator 220.As another example, the direction of the current flowing in thesub-resonator 220 may be determined based on a ratio of a resonancefrequency of the sub-resonator 220 to a resonance frequency of thesource resonator 210.

The resonance frequency of the source resonator 210 may be related to aninductance value L and a capacitance value C of the source resonator210. Similarly, the resonance frequency of the sub-resonator 220 may berelated to an inductance value L and a capacitance value C of thesub-resonator 220.

The magnetic field distribution controller 230 is located in apredetermined area within the source resonator 210. The magnetic fielddistribution controller 230 may control the direction of the currentflowing in the source resonator 210 or in the sub-resonator 220. Themagnetic field distribution controller 230 may control the distributionof the magnetic field formed within the source resonator 210.

The direction of the current flowing in the source resonator 210 and/oror the direction of the current flowing in the sub-resonator 220 may berelated to the ratio of the resonance frequency of the sub-resonator 220to the resonance frequency of the source resonator 210.

The magnetic field distribution controller 230 may control the resonancefrequency of the source resonator 210, or the resonance frequency of thesub-resonator 220. As an example, the magnetic field distributioncontroller 230 may control the resonance frequency of the sourceresonator 210 by changing the capacitance of the source resonator 210.As another example, the magnetic field distribution controller 230 maycontrol the resonance frequency of the sub-resonator 220 by adjustingthe capacitance and the inductance of the sub-resonator 220. Themagnetic field distribution controller 230 may adjust a length and awidth of a line that forms the sub-resonator 220 to control theinductance value of the sub-resonator 220.

The magnetic field distribution controller 230 may control the directionof the current flowing in the source resonator 210, or the magneticfield distribution controller 230 may control the direction of thecurrent flowing in the sub-resonator 220, so that the strength of themagnetic field formed within the source resonator 210 is increased ordecreased.

The magnetic field distribution controller 230 may control thedistribution of the magnetic field so that the magnetic field isuniformly distributed in the source resonator 210. As an example, themagnetic field distribution controller 230 may control the resonancefrequency of the sub-resonator 220, and the magnetic field distributioncontroller 230 may control the magnetic field to be uniformlydistributed in the source resonator 210. The configuration of thesub-resonator 220 will be further described with reference to FIG. 3.

The magnetic field distribution controller 230 may use asub-sub-resonator to control the distribution of the magnetic fieldformed within the source resonator 210. The magnetic field distributioncontroller 230 may control a resonance frequency of thesub-sub-resonator, and the magnetic field distribution controller 230may compensate for the uniform distribution of the magnetic field formedwithin the source resonator 210. The magnetic field distributioncontroller 230 may control the direction of the current flowing in thesub-resonator 220 and a direction of a current flowing in thesub-sub-resonator, and the magnetic field distribution controller 230may control the distribution of the magnetic field. Thesub-sub-resonator may be located in the sub-resonator 220. Thesub-sub-resonator may support the sub-resonator 220, and thesub-sub-resonator may compensate for the distribution of the magneticfield formed within the source resonator 210, so that the magnetic fieldmay be uniformly distributed. The sub-sub-resonator may compensate forthe distribution of the magnetic field adjusted by the sub-resonator 220so that the magnetic field may be uniformly distributed in the sourceresonator 210.

The magnetic field distribution controller 230 may include at least onecoil. The at least one coil may be used to induce the magnetic fieldformed within the source resonator 210 towards the center of the sourceresonator 210. As another example, the magnetic field distributioncontroller 230 may use the at least one coil to control the magneticfield formed within the source resonator 210 to be uniformlydistributed.

The magnetic field distribution controller 230 may control a resonancefrequency of the at least one coil so that a current may flow in the atleast one coil in the same direction as the current flowing in thesource resonator 210.

As an example, a plurality of coils may be located in the center of thesource resonator 210, and the plurality of coils may have respectiveloop structures having different sizes. The magnetic field distributioncontroller 230 may use the plurality of coils having respective loopstructures having different sizes to more precisely control the magneticfield formed within the source resonator 210.

As another example, at least one coil having the same shape as anothercoil may be located in a predetermined position within the sourceresonator 210. The at least one coil having the same shape as the othercoil may be located in various areas within the source resonator 210.Under the control of the magnetic field distribution controller 230, theat least one coil having the same shape as the other coil may increaseor decrease the strength of the magnetic field formed within the sourceresonator 210 in the various areas in which the at least one coil havingthe same shape as the other coil is located.

As another example, the at least one coil may be located in the centerof the source resonator 210. The at least one coil may be formed in aspiral shape. As another example, the at least one coil may have anysuitable shape that is known to one of ordinary skill in the art, andthe at least one coil may adjust the magnetic field formed within thesource resonator 210.

The magnetic field distribution controller 230 may include a pluralityof shielding layers. The plurality of shielding layers may havedifferent sizes and heights located at the center of the sourceresonator 210, and the plurality of shielding layers may have a loopstructure. Due to the plurality of shielding layers being located at thecenter of the source resonator 210 and having the loop structure, themagnetic field distribution controller 230 may induce the magnetic fieldformed within the source resonator 210 to be uniformly distributed. Amagnetic flux of the magnetic field formed within the source resonator210 may be refracted by the plurality of shielding layers, and themagnetic flux of the magnetic field may be more concentrated on thecenter of the source resonator 210.

The magnetic field distribution controller 230 may include a layerformed of a mu negative (MNG) material, a double negative (DNG)material, or a magneto-dielectric material. The magnetic fielddistribution controller 230 may refract the magnetic flux of themagnetic field formed within the source resonator 210, based on thelayer, and the magnetic field distribution controller 230 may induce themagnetic field to be uniformly distributed in the source resonator 210.

The magnetic field distribution controller 230 may adjust widths ofshielding layers laminated in predetermined positions of the sourceresonator 210 and the sub-resonator 220, and the magnetic fielddistribution controller 230 may induce the magnetic field to beuniformly distributed within the source resonator 210. Based on thewidths of the shielding layers, a refractive level of the magnetic fluxof the magnetic field formed within the source resonator 210 may bechanged. Accordingly, the magnetic field distribution controller 230 mayadjust the widths of the shielding layers to control the magnetic fieldto be uniformly distributed within the source resonator 210.

The source resonator 210 may be implemented as a pad-type resonator, andthe target device may be positioned on the source resonator 210. In thisexample, a gap between the source resonator 210 and the target devicemay be less than 2 or 3 centimeters (cm). Accordingly, a parasiticcapacitance may be formed between the source resonator 210 and thetarget device. The parasitic capacitance may influence the resonancefrequency of the source resonator 210. The magnetic field distributioncontroller 230 may adjust widths and thicknesses of the shielding layerslaminated in predetermined positions of the source resonator 210 and thesub-resonator 220 to offset a change in the resonance frequency of thesource resonator 210 due to the parasitic capacitance formed between thesource resonator 210 and the target device.

FIG. 3 illustrates an example of a wireless power transmitter 300. Asource resonator forms a magnetic coupling with a target resonator. Thesource resonator wirelessly transmits a power to the target device viathe magnetic coupling. As illustrated in FIG. 3, the source resonatorincludes a first transmission line (not identified by a referencenumeral in FIG. 3, but formed by various elements in FIG. 3 as discussedbelow), a first conductor 321, a second conductor 322, and a firstcapacitor 330. Although one first capacitor 330 is illustrated in FIG.3, a plurality of first capacitors 330 may be provided.

The first capacitor 330 is inserted in series between a first signalconducting portion 311 and a second signal conducting portion 312 in thefirst transmission line. An electric field is confined within the firstcapacitor 330. The first transmission line may include at least oneconductor in an upper portion of the first transmission line, and atleast one conductor in a lower portion of the first transmission line.Current may flow through the at least one conductor disposed in theupper portion of the first transmission line. The at least one conductordisposed in the lower portion of the first transmission line may beelectrically grounded. For example, in the example in FIG. 3, aconductor disposed in an upper portion of the first transmission line isseparated into the first signal conducting portion 311 and the secondsignal conducting portion 312. A first ground conducting portion 313 isa conductor disposed in a lower portion of the first transmission line.

The source resonator of FIG. 3 has a two-dimensional (2D) structure. Thefirst transmission line includes the first signal conducting portion 311and the second signal conducting portion 312. The first signalconducting portion 311 and the second signal conducting portion 312 arelocated in the upper portion of the first transmission line. Inaddition, the first transmission line includes the first groundconducting portion 313 in the lower portion of the first transmissionline. The first signal conducting portion 311 and the second signalconducting portion 312 face the first ground conducting portion 313.Current flows through the first signal conducting portion 311 and thesecond signal conducting portion 312.

One end of the first signal conducting portion 311 is connected to oneend of the first conductor 321, the other end of the first signalconducting portion 311 is connected to one end of the first capacitor330, and the other end of the first conductor 321 is connected to oneend of the first ground conducting portion 313. One end of the secondsignal conducting portion 312 is connected to one end of the secondconductor 322, the other end of the second signal conducting portion 312is connected to the other end of the first capacitor 330, and the otherend of the second conductor 322 is connected to the other end of thefirst ground conducting portion 313. Accordingly, the first signalconducting portion 311, the second signal conducting portion 312, thefirst ground conducting portion 313, the first conductor 321, and thesecond conductor 322 are connected to each other to form an electricallyclosed loop structure. Thus, the source resonator of FIG. 3 has anelectrically closed-loop structure. The term “loop structure” includes apolygonal structure, a circular structure, a rectangular structure, andany other geometrical structure that is closed, i.e., that does not haveany opening in its perimeter. The expression “having a loop structure”indicates a structure that is electrically closed, i.e., a structurethat forms a closed electrical circuit.

The first capacitor 330 is inserted into an intermediate portion of thefirst transmission line. In the example in FIG. 3, the first capacitor330 is inserted into a space between the first signal conducting portion311 and the second signal conducting portion 312. The first capacitor330 may be a lumped element capacitor, a distributed element capacitor,or any other type of capacitor known to one of ordinary skill in theart. For example, a distributed element capacitor may include azigzagged conductor line and a dielectric material having a highpermittivity disposed between parallel portions of the zigzaggedconductor line.

The first capacitor 330 inserted into the first transmission line in thespace between the first signal conducting portion 311 and the secondsignal conducting portion 312 may cause the source resonator may have acharacteristic of a metamaterial. A metamaterial is a material having apredetermined electrical property that is not found in nature, and thusmay have an artificially designed structure. All materials existing innature have a magnetic permeability or a permittivity. Most materialshave a positive magnetic permeability and/or a positive permittivity.

For most materials, a right-hand rule may be applied to an electricfield, a magnetic field, and a Poynting vector of the materials, so thematerials may be referred to as right-handed materials (RHMs). However,a metamaterial has a magnetic permeability and/or a permittivity that isnot found in nature, and may be classified into an epsilon negative(ENG) material, a mu negative (MNG) material, a double negative (DNG)material, a negative refractive index (NRI) material, a left-handed (LH)material, and the other metamaterial classifications known to one ofordinary skill in the art based on a sign of the magnetic permeabilityand/or permittivity of the metamaterial.

If the first capacitor 330 is a lumped element capacitor and acapacitance of the first capacitor 330 is appropriately determined, thesource resonator may have a characteristic of a metamaterial. If sourceresonator is caused to have a negative magnetic permeability byappropriate adjusting the capacitance of the first capacitor 330, thesource resonator may also be referred to as an MNG resonator. Variouscriteria may be used to determine the capacitance of the first capacitor330. For example, the various criteria may include a criterion forenabling the source resonator to have a characteristic of ametamaterial, a criterion for enabling the source resonator to have anegative magnetic permeability at a target frequency, a criterion forenabling the source resonator to have a zeroth order resonancecharacteristic at a target frequency, and any other suitable criterion.Based on any one or any combination of the aforementioned criteria, thecapacitance of the first capacitor 330 may be appropriately determined.

The source resonator, also referred to as the MNG resonator, may have azeroth order resonance characteristic of having a resonance frequencywhen a propagation constant is “0”. If the MNG resonator has the zerothorder resonance characteristic, the resonance frequency of the MNGresonator is independent of a physical size of the MNG resonator. Bychanging the capacitance of the first capacitor 330, the resonancefrequency of the MNG resonator may be changed without changing thephysical size of the MNG resonator.

In a near field, the electric field is concentrated in the firstcapacitor 330 inserted into the first transmission line, causing themagnetic field to become dominant in the near field. The MNG resonatorhas a relatively high Q-factor when the first capacitor 330 is a lumpedcapacitor, thereby increasing a power transmission efficiency. TheQ-factor indicates a level of an ohmic loss or a ratio of a reactancewith respect to a resistance in the wireless power transmission. As willbe understood by one of ordinary skill in the art, the efficiency of thewireless power transmission will increase as the Q-factor increases.

Although not illustrated in FIG. 3, a magnetic core passing through theMNG resonator may be provided to increase a power transmission distance.

Referring to FIG. 3, a sub-resonator includes a second transmission line(not identified by a reference numeral in FIG. 3, but formed by variouselements in FIG. 3 as discussed below), a third conductor 351, a fourthconductor 352, and a second capacitor 360. Although one second capacitor360 is illustrated in FIG. 3, a plurality of second capacitors 360 maybe provided.

The second capacitor 360 is inserted between a third signal conductingportion 341 and a fourth signal conducting portion 342 in the secondtransmission line, and an electric field is confined in the secondcapacitor 360. In the example in FIG. 3, the second capacitor 360 isconnected in series between the third signal conducting portion 341 andthe fourth signal conducting portion 342.

As illustrated in FIG. 3, the sub-resonator has a 2D structure. Thesecond transmission line includes the third signal conducting portion341 and the fourth signal conducting portion 342 in an upper portion ofthe second transmission line, and a second ground conducting portion 343in a lower portion of the second transmission line. The third signalconducting portion 341 and the fourth signal conducting portion 342 facethe second ground conducting portion 343. Current flows through thethird signal conducting portion 341 and the fourth signal conductingportion 342.

One end of the third signal conducting portion 341 is connected to oneend of the third conductor 351, the other end of the third signalconducting portion 341 is connected to one end of the second capacitor360, and the other end of the third conductor 351 is connected to oneend of the second ground conducting portion 343. One end of the fourthsignal conducting portion 342 is connected to one end of the fourthconductor 352, the other end of the fourth signal conducting portion 342is connected to the other end of the second capacitor 360, and the otherend of the fourth conductor 352 is connected to the other end of thesecond ground conducting portion 343. Accordingly, the third signalconducting portion 341, the fourth signal conducting portion 342, thesecond ground conducting portion 343, the third conductor 351, and thefourth conductor 352 are connected to each other to form an electricallyclosed loop structure. Thus, the sub-resonator of FIG. 3 has anelectrically closed loop structure. The term “loop structure” includes apolygonal structure, a circular structure, a rectangular structure, acrossed loop structure, and any other geometrical structure that isclosed, i.e., that does not have any opening in its perimeter. Theexpression “having a loop structure” indicates a structure that iselectrically closed, i.e., a structure that forms a closed electricalcircuit.

A magnetic field distribution controller (not illustrated in FIG. 3, butillustrated in FIG. 2 and described above in connection with FIG. 3) mayadjust a resonance frequency of the sub-resonator based on a value ofthe second capacitor 360, and a length and a width of the secondtransmission line formed by the third signal conducting portion 341, thefourth signal conducting portion 342, and the second ground conductingportion 343. Thus, the resonance frequency of the sub-resonator may beadjusted to differ from a resonance frequency of the source resonator bya predetermined value.

The magnetic field distribution controller may adjust the value of thesecond capacitor 360 to adjust the resonance frequency of thesub-resonator. Accordingly, the magnetic field distribution controllermay adjust the value of the second capacitor 360 to adjust the resonancefrequency of the sub-resonator to be greater than or less than theresonance frequency of the source resonator so that a magnetic fieldformed in the center of the source resonator may have substantially thesame strength as a magnetic field formed outside the source resonator.

FIGS. 4 through 8 illustrate examples of resonators. A source resonatorincluded in a wireless power transmitter may have a structure asillustrated in FIGS. 4 through 8.

FIG. 4 illustrates an example of a resonator 400 having athree-dimensional (3D) structure. Referring to FIG. 4, the resonator 400having the 3D structure includes a transmission line (not identified bya reference numeral in FIG. 4, but formed by various elements in FIG. 4as discussed below) and a capacitor 420. The transmission line includesa first signal conducting portion 411, a second signal conductingportion 412, and a ground conducting portion 413. The capacitor 420 isconnected in series between the first signal conducting portion 411 andthe second signal conducting portion 412 of the transmission line. Anelectric field is confined within the capacitor 420.

As illustrated in FIG. 4, the resonator 400 has a 3D structure. Thetransmission line includes the first signal conducting portion 411 andthe second signal conducting portion 412 in an upper portion of theresonator 400, and the ground conducting portion 413 in a lower portionof the resonator 400. The first signal conducting portion 411 and thesecond signal conducting portion 412 face the ground conducting portion413. In the example in FIG. 4, current flows in an x direction throughthe first signal conducting portion 411 and the second signal conductingportion 412, thereby creating a magnetic field H(ω) in a −y direction.As another example, a current may flow in a −x direction through thefirst signal conducting portion 411 and the second signal conductingportion 412, thereby creating a magnetic field H(ω) in a +y direction.

One end of the first signal conducting portion 411 is connected to oneend of a conductor 442, the other end of the first signal conductingportion 411 is connected to one end of the capacitor 420, and the otherend of the conductor 442 is connected to one end of the groundconducting portion 413. One end of the second signal conducting portion412 is connected to one end of a conductor 441, the other end of thesecond signal conducting portion 412 is connected to the other end ofthe capacitor 420, and the other end of the conductor 441 is connectedto the other end of the ground conducting portion 413. Accordingly, thefirst signal conducting portion 411, the second signal conductingportion 412, the ground conducting portion 413, and the conductors 441and 442 are connected to each other to form an electrically closed loopstructure. Thus, the resonator 400 of FIG. 4 has an electrically closedloop structure. The term “loop structure” includes a polygonalstructure, a circular structure, a rectangular structure, and any othergeometrical structure that is closed, i.e., that does not have anyopening in its perimeter. The expression “having a loop structure”indicates a structure that is electrically closed, i.e., a structurethat forms a closed electrical circuit.

As shown in FIG. 4, the capacitor 420 is inserted between the firstsignal conducting portion 411 and the second signal conducting portion412. The capacitor 420 may a lumped element capacitor, a distributedelement capacitor, or any other type of capacitor known to one ofordinary skill in the art. For example, a distributed element capacitormay include a zigzagged conductor line and a dielectric material havinga relatively high permittivity disposed between parallel portions of thezigzagged conductor line.

The resonator 400 with the capacitor 420 inserted into the transmissionline may have a characteristic of a metamaterial. If the capacitor 420is a lumped element capacitor and a capacitance of the capacitor 420 isappropriately determined, the resonator 400 may have a characteristic ofa metamaterial. If the capacitance of the capacitor 420 is adjustedcause the resonator 400 to have a negative magnetic permeability, theresonator 400 may also be referred to as an MNG resonator. Variouscriteria may be used to determine the capacitance of the capacitor 420.For example, the various criteria may include a criterion for enablingthe resonator 400 to have a characteristic of a metamaterial, acriterion for enabling the resonator 400 to have a negative magneticpermeability at a target frequency, a criterion for enabling theresonator 400 to have a zeroth order resonance characteristic at atarget frequency, and any other suitable criterion. The capacitance ofthe capacitor 420 may be appropriately determined based on any one orany combination of the aforementioned criteria.

The resonator 400, also referred to as the MNG resonator 400, may have azeroth order resonance characteristic of having a resonance frequencywhen a propagation constant is “0”. If the MNG resonator 400 has thezeroth order resonance characteristic, the resonance frequency of theMNG resonator 400 is independent of a physical size of the MNG resonator400. By changing the capacitance of the capacitor 420, the resonancefrequency of the MNG resonator 400 may be changed without changing thephysical size of the MNG resonator 400.

In the MNG resonator 400 of FIG. 4, in a near field, the electric fieldis concentrated in the capacitor 420 inserted into the transmissionline, causing the magnetic field to become dominant in the near fielddue to the electric field being concentrated in the capacitor 420. TheMNG resonator 400 having the zeroth order resonance characteristic has acharacteristic similar to a magnetic dipole, so the magnetic field isdominant in the near field. A relatively small electric field isproduced by the insertion of the capacitor 420, and that small electricis concentrated in the capacitor 420, so the magnetic field becomes evenmore dominant in the near field. The MNG resonator 400 has a relativelyhigh Q-factor when the capacitor 420 is a lumped element, whichincreases a power transmission efficiency.

The MNG resonator 400 includes a matcher 430 for performing impedancematching. The matcher 430 adjusts the strength of magnetic field of theMNG resonator 400, and determines an impedance of the MNG resonator 400.Current flows into and/or out of the MNG resonator 400 via a connector440 connected to the ground conducting portion 413 or the matcher 430.

For example, as shown in FIG. 4, the matcher 430 is positioned withinthe loop structure of the resonator 400. The physical shape of thematcher 430 is changed to adjust the impedance of the resonator 400. Thematcher 430 includes a conductor 431 for performing impedance matchingspaced apart from the ground conducting portion 413 by a distance h.Adjusting the distance h changes the impedance of the resonator 400.

Although not illustrated in FIG. 4, a controller may be provided tocontrol the matcher 430. For example, the physical shape of the matcher430 may be changed based on a control signal generated by thecontroller. For example, the distance h between the conductor 431 of thematcher 430 and the ground conducting portion 413 may be increased ordecreased in response to the control signal. Accordingly, the physicalshape of the matcher 430 may be changed to adjust the impedance of theresonator 400. The distance h between the conductor 431 of the matcher430 and the ground conducting portion 413 may be adjusted using avariety of methods. As one example, the matcher 430 may include aplurality of conductors located at difference distances h from theground conducting portion 413, and the distance h may be adjusted byadaptively activating one of the conductors located at a desireddistance h from the ground conducting portion 413. As another example,the distance h may be adjusted by moving the physical location of theconductor 431 up and down. The distance h may be controlled based on thecontrol signal of the controller. The controller may generate thecontrol signal using various factors.

In the example in FIG. 4, the matcher 430 includes a passive element,i.e., the conductor 431. However, in another example, the matcher 430may include an active element. The active element may be a diode, atransistor, or any other suitable active element known to one ofordinary skill in the art. If an active element is included in thematcher 430, the active element may be controlled based on the controlsignal generated by the to adjust the impedance of the resonator 400based on the control signal. For example, a diode may be included in thematcher 430 as an active element, and the impedance of the resonator 400may be adjusted by turning the diode ON and OFF.

Although not illustrated in FIG. 4, a magnetic core passing through MNGresonator 400 to increase a power transmission distance.

FIG. 5 illustrates an example of a bulk-type resonator 500 for wirelesspower transmission. A bulk-type resonator is a resonator in which atleast two current-carrying elements are seamlessly connected to eachother by being integrally formed as a single unit. Referring to FIG. 5,a first signal conducting portion 511, a conductor 542, a groundconducting portion 513, a conductor 541, and a second signal conductingportion 512 are integrally formed as a single unit instead of beingseparately manufactured and then connected to each other.

If, for example, the second signal conducting portion 512 and theconductor 541 were separately manufactured and then connected to eachother, a loss of conduction might occur at a seam 550. To avoid such aloss of conduction in the bulk-type resonator 500, the first signalconducting portion 511, the conductor 542, the ground conducting portion513, the conductor 541, and the second signal conducting portion 512 areconnected to each other without using separate seams. In other words,the first signal conducting portion 511, the conductor 542, the groundconducting portion 513, the conductor 541, and the second signalconducting portion 512 are seamlessly connected to each other byintegrally forming these elements as a single unit. Accordingly, aconduction loss caused by seams that would otherwise be required toconnect these elements together, such as the seam 550 discussed above,is eliminated. Although in this example, the first signal conductingportion 511, the conductor 542, the ground conducting portion 513, theconductor 541, and the second signal conducting portion 512 areintegrally formed as a single unit, only some of these elements may beintegrally formed as a single unit.

FIG. 6 illustrates an example of a hollow-type resonator 600 forwireless power transmission. Referring to FIG. 6, a first signalconducting portion 611, a second signal conducting portion 612, a groundconducting portion 613, and conductors 641 and 642 each are hollow,i.e., they each have an empty space inside. A capacitor 620 is insertedin series between the first signal conducting portion 611 and the secondsignal conducting portion 612, and a matcher 630 for impedance matchingis provided on the ground conducting portion 613.

At a given resonance frequency, an alternating current (AC) may bemodeled as flowing in only a portion of the first signal conductingportion 611, the second signal conducting portion 612, the groundconducting portion 613, and the conductors 641 and 642 between the outersurface of these elements and a level called the skin depth. If a depthof each of the first signal conducting portion 611, the second signalconducting portion 612, the ground conducting portion 613, and theconductors 641 and 642 is significantly deeper than a corresponding skindepth at the given resonance frequency, the portions of these elementsdeeper than the skin depth will be ineffective since substantially nocurrent will flow in these portions. The ineffective portions increase aweight and manufacturing costs of the resonator 600.

Accordingly, at the given resonance frequency, the depth of each of thefirst signal conducting portion 611, the second signal conductingportion 612, the ground conducting portion 613, and the conductors 641and 642 is determined based on the corresponding skin depth of each ofthe first signal conducting portion 611, the second signal conductingportion 612, the ground conducting portion 613, and the conductors 641and so that ineffective portions deeper than the corresponding skindepth are eliminated, causing the resonator 600 to become lighter inweight, and causing the manufacturing costs of the resonator 600 todecrease.

For example, as shown in FIG. 6, a depth of the second signal conductingportion 612 may d mm, and d may be calculated according to the followingEquation 1:

$\begin{matrix}{d = \frac{1}{\sqrt{\pi\; f\;\mu\;\sigma}}} & (1)\end{matrix}$

In Equation 1, f denotes a resonance frequency, μ denotes a magneticpermeability of a material of which the first signal conducting portion611, the second signal conducting portion 612, the ground conductingportion 613, and the conductors 641 and 642 are made, and σ denotes anelectrical conductivity of the material of which the first signalconducting portion 611, the second signal conducting portion 612, theground conducting portion 613, and the conductors 641 and 642 are made.

For example, if the first signal conducting portion 611, the secondsignal conducting portion 612, the ground conducting portion 613, andthe conductors 641 and 642 are made of copper, which has a magneticpermeability μ of 1.257×10⁻⁶ henries per meter (H·m⁻¹) and an electricalconductivity σ of 5.8×10⁷ siemens per meter (S·m⁻¹), the skin depth dcalculated from Equation 1 is about 0.6 mm at a resonance frequency f of10 kHz, or about 0.006 mm at a resonance frequency f of 100 MHz.

FIG. 7 illustrates an example of a resonator 700 for wireless powertransmission configured as a parallel-sheet type resonator. Referring toFIG. 7, a first signal conducting portion 711, a second signalconducting portion 712, a ground conducting portion 713, and conductors741 and 742 included in the resonator 700 are each configured as aplurality of parallel sheets. A capacitor 720 is inserted in seriesbetween the first signal conducting portion 711 and the second signalconducting portion 712, and a matcher 730 for impedance matching isprovided on the ground conducting portion 713.

The first signal conducting portion 711, the second signal conductingportion 712, the ground conducting portion 713, and the conductors 741and 742 are typically made of a material that is not a perfectconductor, and therefore have a resistance. Due to the resistance, anohmic loss occurs in the resonator 700, which decrease a O-factor and acoupling effect.

By configuring each of the first signal conducting portion 711, thesecond signal conducting portion 712, the ground conducting portion 713,and the conductors 741 and 742 as a plurality of parallel sheets, theohmic loss maybe decreased, thereby increasing the Q-factor and thecoupling effect.

Referring to a portion 770 indicated by a circle, each of the firstsignal conducting portion 711, the second signal conducting portion 712,the ground conducting portion 713, and the conductors 741 and 742include a plurality of conductor lines configured as a plurality ofsheets disposed parallel to each other and shorted together at an endportion of each of the first signal conducting portion 711 and thesecond signal conducting portion 712. This causes resistances of theconductor lines to be connected in parallel, causing a total resistanceof the conductor lines to be less than a resistance of each of theconductor lines, thereby decreasing the ohmic loss, thereby increasingthe Q-factor and the coupling effect.

FIG. 8 illustrates an example of a resonator 800 for wireless powertransmission that includes a distributed element capacitor. Referring toFIG. 8, a distributed element capacitor 820 is included in the resonator800 for wireless power transmission. A lumped element capacitor has arelatively high equivalent series resistance (ESR). The ESR causes anohmic loss that decreases a Q factor and a coupling effect. A variety oftechniques may be used to decrease the ESR of a capacitor. In thisexample, by using the distributed element capacitor 820 instead of alumped element capacitor, the ESR is decreased, thereby decreasing theohmic loss caused by the ESR and increasing a Q-factor and a couplingeffect.

In the example in FIG. 8, the distributed element capacitor 820 has azigzagged structure configured as a zigzagged conductor line and adielectric material having a high permittivity disposed between parallelportions of the zigzagged conductor line.

Employing the distributed element capacitor 820 having the zigzaggedstructure decreases an ohmic loss caused by the ESR of the distributedelement capacitor 820. The distributed element capacitor 820 having thezigzagged structure may be modeled as a plurality of lumped elementcapacitors connected in parallel. Since a total resistance of aplurality of resistances connected in parallel is less than each of theresistances, the total ESR of a plurality of lumped element capacitorsconnected in parallel is less than an ESR of each of the lumped elementcapacitors. For example, by employing ten 1 pF capacitors each connectedin parallel instead of employing a single 10 pF capacitor, it ispossible to decrease the ohmic loss caused by the ESR because the totalESR of the ten 1 pF capacitors connected in parallel is one-tenth theESR of the single 10 pF capacitor.

FIG. 9 illustrates an example of an equivalent circuit of the resonatorof FIG. 3. The resonator of FIG. 3 may be modeled as the equivalentcircuit of FIG. 9. In the equivalent circuit of FIG. 9, L_(R) denotes aninductance of the resonator, C_(R) denotes a capacitance of theresonator, and C_(L) denotes a lumped element capacitor inserted inapproximately the middle of one of the transmission lines of theresonator of FIG. 3.

In this example, the resonator of FIG. 3 has a zeroth order resonancecharacteristic in which the resonator of FIG. 3 has a resonancefrequency ω_(MZR) when a propagation constant is “0”. The resonancefrequency ω_(MZR) may be expressed by the following Equation 2.

$\begin{matrix}{\omega_{MZR} = \frac{1}{\sqrt{L_{R}C_{L}}}} & (2)\end{matrix}$

In Equation 2, MZR denotes a mu zero resonator. The capacitance C_(R) ofthe resonator is negligible compared to the capacitance C_(L) of thelumped element capacitor, so it is omitted from Equation 2.

Referring to Equation 2, the resonance frequency ω_(MZR) of theresonator of FIG. 3 depends on L_(R)C_(L). Since the resonator of FIG. 3has a zeroth order resonance characteristic in this example, a physicalsize of the resonator of FIG. 3 and the resonance frequency ω_(MZR) ofthe resonator of FIG. 3 are independent of each other, and therefore thephysical size of the resonator of FIG. 3 may be reduced without changingthe resonance frequency ω_(MZR).

FIG. 10 illustrates an example of an apparatus 1000 including anovertemperature, overvoltage, and overcurrent protection scheme. Theapparatus 1000 may be a radio frequency power amplifier, or a wirelesspower transmitter, or a portion of a wireless power transmitter.

The apparatus 1000 provides a protection scheme to prevent a breakdownfrom occurring as a result of an overvoltage, an overcurrent, or anovertemperature in a wireless-coupled power apparatus.

A coupling characteristic of a wireless power transmission system maychange depending on (1) a distance between a wireless power transmitterand a wireless power receiver, and (2) a position of each of thewireless power transmitter and the wireless power receiver.

Generally, improper matching of impedances may occur between thewireless power transmitter and a transmitting antenna or a resonator.The improper matching of impedances may cause an increase in a magnitudeof a voltage applied across a power device of the wireless powertransmitter, for example, the apparatus 1000, and may result in abreakdown of the power device. Accordingly, there is a need for acircuit that can prevent a breakdown of a power device resulting fromimproper impedance matching resulting from a change in a couplingcharacteristic between devices transmitting power wirelessly.

The apparatus 1000 includes an input matching network 1010, a powerdevice 1020, an output matching network 1030, an overvoltage protectingunit 1040, an overcurrent protecting unit 1050, an overtemperatureprotecting unit 1060, and a control unit 1070.

The input matching network 1010 is a circuit for performing impedancematching with a circuit, for example, a signal generator, be connectedto an RF input terminal 1002 of the apparatus 1000.

The power device 1020 is a wireless power amplifier. The power device1020 may be a bipolar junction transistor, or a Field Effect Transistor(FET), or any other type of transistor that is known to one of ordinaryskill in the art. The power device 1020 includes a first terminal 1022,a second terminal 1024, and a third terminal 1026.

If the power device 1020 is an NPN bipolar junction transistor, thefirst terminal 1022 is a base, the second terminal 1024 is a collector,and the third terminal 1026 is an emitter.

If the power device 1020 is an N-channel FET, the first terminal 1022 isa gate, the second terminal 1024 is a drain, and the third terminal 1026is a source.

The output matching network 1030 is a circuit for performing impedancematching with a circuit, for example, a signal generator, connected toan output terminal 1004 of the apparatus 1000.

The overvoltage protecting unit 1040 detects a voltage applied acrossthe power device 1020, and automatically turns the apparatus 1000 OFFwhen an overvoltage is applied across the power device 1020. Theovervoltage protecting unit 1040 automatically turns the apparatus10000N and OFF using a control characteristic exhibiting hysteresis.

The overcurrent protecting unit 1050 detects a current flowing throughthe power device 1020, and automatically turns the apparatus 1000 OFFwhen an overcurrent flows through the power device 1020. The overcurrentprotecting unit 1040 automatically turns the apparatus 10000N and OFFusing a control characteristic exhibiting hysteresis.

The overtemperature protecting unit 1060 adjusts a level of a biasvoltage of the power device 1020 using a thermistor to prevent abreakdown or a decrease in a performance of the power device 1020 and/orthe apparatus due to a high temperature.

The control unit 1070 includes an OR gate 1072 and a NAND gate 1074.

The OR gate 1072 receives as inputs an output signal of the overvoltageprotecting unit 1040, and an output signal of the overcurrent protectingunit 1050. That is, inputs of the OR gate 1072 are connected to anoutput of the overvoltage protecting unit 1040 and an output of theovercurrent protecting unit 1050.

The OR gate 1072 outputs a signal indicating that the apparatus 1000 isto be turned OFF when the output signal of the overvoltage protectingunit 1040 and/or the output signal of the overcurrent protecting unit1050 is a signal indicating that the power device 1020 or the apparatus1000 is to be turned OFF. For example, the signal indicating that thepower device 1020 or the apparatus 1000 is to be turned OFF may be anovervoltage detection signal or an overcurrent detection signal, whichwill be hereinafter referred to as an OFF signal. Otherwise, the OR gate1072 outputs a signal indicating that the apparatus 1000 is to be turnedON, which will be hereinafter referred to as an ON signal.

The NAND gate 1074 as inputs the output signal of the OR gate 1072 andan RF input signal. That is, inputs of the NAND gate 1074 are connectedto an output of the OR gate 1072 and the RF input terminal 1002.

The NAND gate 1074 outputs an RF input signal received from the RF inputterminal 1002 when the output signal of the OR gate 1072 is the ONsignal, and does not output the RF input signal when the output signalof the OR gate 1072 is the OFF signal. That is, the NAND gate 1072blocks the RF input signal from being input to the power device 1020when the output signal of the OR gate 1072 is the OFF signal.

Connections among the elements included in the apparatus 1000 will nowbe described. An output of the control unit 1070 is connected to aninput of the input matching network 1010. An output of the inputmatching network 1010 is connected to the first terminal 1022 of thepower device 1020. The second terminal 1024 of the power device 1020 isconnected to an input of the output matching network 1030. An output ofthe output matching network 1030 is connected to the output terminal1004 of the apparatus 1000. The third terminal 1026 of the power device1020 is connected to a ground. An input of the overvoltage protectingunit 1040 is connected to the second terminal 1024 of the power device1020. An input of the overcurrent protecting unit 1050 is connected tothe second terminal 1024 of the power device 1020. An input of theovertemperature protecting unit 1060 is connected to the second terminal1024 of the power device 1020. An output of the overtemperatureprotecting unit 1060 is connected to the first terminal 1022 of thepower device 1020.

FIG. 11 illustrates an example of the overvoltage protecting unit 1040of FIG. 10. The overvoltage protecting unit 1040 includes a firstresistive divider 1110, a rectifier 1120, a second resistive divider1130, a DC supply 1140, and a comparator 1150.

The first resistive divider 1110 outputs a first divided voltage bydividing an input voltage. The input voltage is a voltage of the secondterminal 1024 of the power device 1020. Generally, a voltage appliedacross the power device 1020 operating as a high efficiency RF poweramplifier has a half-sinusoidal form. The first resistive divider 1110has a high impedance and samples the voltage without influencing a poweramplification performance of the power device. The first resistivedivider 1110 includes a first resistor 1112 and a second resistor 1114.The first resistor 1112 is connected to an input of the first resistivedivider 1110 and an input of the rectifier 1120. The second resistor1114 is connected to the first resistor 1112 at the connection to theinput of the rectifier 1120, and a ground.

The rectifier 1120 outputs a rectified voltage by rectifying the firstdivided voltage. That is, the rectifier 1120 rectifies the voltagesampled by the first resistive divider 1110. The rectifier 1120 includesa diode 1122 and a capacitor 1124. An anode of the diode 1122 isconnected to the first resistive divider 1110 at the connection betweenthe first resistor 1112 and the second resistor 1114. A cathode of thediode 1122 is connected to an input of the second resistive divider1130. The capacitor 1124 is connected to the cathode of the diode 1122and a ground.

The second resistive divider 1130 outputs a second divided voltage bydividing the voltage rectified by the rectifier 1120. The secondresistive divider 1130 includes a third resistor 1132 and a fourthresistor 1134. The third resistor 1132 is connected to an output of therectifier 1120, and a positive (+) terminal of the comparator 1150. Thefourth resistor 1134 is connected to the third resistor 1132 at theconnection to the positive (+) terminal of the comparator 1150, and aground.

The DC supply 1140 applies a DC voltage to a negative (−) terminal ofthe comparator 1150. The DC supply 1140 is connected to a ground and thenegative (−) terminal of the comparator 1150.

The comparator 1150 receives as inputs the second divided voltagethrough the + terminal, and the DC voltage through the − terminal.

A case in which a rectified voltage or a second divided voltage isgreater than a reference value indicates that the apparatus 1000 needsto be protected from an overvoltage. In this case, when a differencebetween the rectified voltage or the second divided voltage and areference voltage level, for example, a voltage level of a DC voltage,is small, that is, when the rectified voltage or the second dividedvoltage is slightly higher or lower than the reference voltage level, itmay be difficult to determine whether the apparatus 1000 requiresprotection. Accordingly, the comparator 1150 has hysteresis.

That is, the comparator 1150 changes a control signal to be output bythe comparator 1150 to a first control signal when a difference betweena voltage input through the + terminal and a voltage input through the −terminal is greater than or equal to an ON-level, and changes thecontrol signal to be output by the comparator 1150 to a second controlsignal when the difference between the voltage input through the +terminal and the voltage input through the − terminal is less than orequal to an OFF-level. The first control signal is an OFF signal, andthe second control signal is an ON signal.

The ON-level of the comparator 1150 may be lower than a breakdownvoltage of the power device 1020, for example, at least 5% lower.

The OFF-level of the comparator 1150 may be determined based on anoperational frequency of the power device 1020, a power level of thepower device 1020, or any other suitable criterion indicating asituation which the apparatus 1000 requires protection. When theoperational frequency of the power device 1020 is relatively high, orthe power level of the power device 1020 is relatively great, adifference between the ON-level and the OFF-level may need to berelatively great in order to prevent an undesired operation.

The control unit 1070 blocks the RF input signal received from the RFinput terminal 1002 from being input to the power device 1020 when thecontrol signal from the comparator 1150 is the first control signal,i.e., the OFF signal.

Accordingly, the overvoltage protecting unit 1040 protects the powerdevice 1020 when the power device 1020 is operated at an overvoltage,such as an overvoltage caused by improper matching of wireless-coupledpower devices.

FIGS. 12A and 12B illustrate an example of an operation of thecomparator 1150 of FIG. 11 having hysteresis. Solid lines in a graph1210 of FIG. 12A indicate voltages that are rectified and output by therectifier 1120 over time. Broken lines in the graph 1210 indicatereference voltages that are output by the DC supply 1140. A rectifiedvoltage is input to the comparator 1150 through the + terminal. Areference voltage is input to the comparator 1150 through the −terminal. A graph 1220 of FIG. 12B indicates a voltage output from thecomparator 1150 according to a voltage output from the rectifier 1120.

The comparator 1150 outputs a voltage y₁ when the voltage output by therectifier 1120 is less than a voltage x₂. Although the voltage output bythe rectifier 1120 may gradually increase, the comparator 1150 continuesto output the voltage y₁ until the voltage output by the rectifier 1120reaches the voltage x₂.

When the voltage output by the rectifier 1120 reaches the voltage x₂,the voltage output by the comparator 1150 changes to a voltage y₂. Thecomparator 1150 continues output the voltage y₂ until the voltage outputby the rectifier 1120 reaches a value less than or equal to a voltagex₁. When the voltage output by the rectifier 1120 reaches a value lessthan or equal to the voltage x₁, the voltage output by the comparator1150 changes to the voltage y₁.

That is, when a value obtained by subtracting the reference voltageoutput by the DC supply 1140 from the voltage output by the rectifier1120 is greater than or equal to a value α₂, the comparator 1150 outputsa first control signal, that is, an OFF signal, having the voltage y₂.

Also, when a value obtained by subtracting the voltage output by therectifier 1120 from the reference voltage output by the DC supply 1140is greater than or equal to a value α₁, the comparator 1150 outputs asecond control signal, that is, an ON signal, having the voltage y₁.

In other cases, that is, when the value obtained by subtracting thereference voltage output by the DC supply 1140 from the voltage outputby the rectifier 1120 is less than the value α₂, or when the valueobtained by subtracting the voltage output by the rectifier 1120 fromthe reference voltage output by the DC supply 1140 is less than thevalue α₁, the comparator 1150 continues to output a signal that iscurrently being output. That is, when the voltage output by therectifier 1120 and the reference voltage output by the DC supply 1140are within a predetermined range, the signal being output by thecomparator 1150 does not change.

FIG. 13 illustrates an example of the overcurrent protecting unit 1050of FIG. 10. The overcurrent protecting unit 1050 includes a resistivedivider 1310, a first DC supply 1320, a first comparator 1330, a switch1340, an amplifier 1350, a second DC supply 1360, and a secondcomparator 1370.

Generally, the power device 1020 has an ON-resistance, which may berepresented as a virtual resistor 1302 having a resistance R_(ON).Accordingly, in a high-efficiency power amplifier in which the powerdevice 1020 operates as a switch, a low voltage i_(sw)R_(ON) is appliedacross the power device 1020 due to a current i_(sw) flowing through thepower device 1020, for example, between the second terminal 1024 and thethird terminal 1026, when the power device 1020 is switched on.

The voltage applied across the power device 1020 is proportional to amagnitude of the current i_(sw) flowing through the power device 1020.Accordingly, when an overcurrent flows through the power device 1020, alevel of the voltage applied across the power device 1020 increases.

In order to detect an overcurrent, a level of a voltage applied acrossthe power device 1020 when the apparatus 1000 or the power device 1020is turned ON may be used. Accordingly, the switch 1340 is provided toenable the overcurrent protecting unit 1050 to sense the level of thevoltage applied across the power device 1020 when the apparatus 1000 orthe power device 1020 is turned ON.

The resistive divider 1310 outputs a divided voltage by dividing a firstinput voltage. The first input voltage is a voltage of the secondterminal 1024 of the power device 1020. The resistive divider 1310includes a first resistor 1312 and a second resistor 1314. The firstresistor 1312 is connected to an input of the switch 1340 and a ground.The second resistor 1314 is connected to an input of the resistivedivider 1310, which is connected to the second terminal 1024 of thepower device 1020, and the first resistor 1312 at the connection to theinput of the switch 1340.

The first DC supply 1320 outputs a first DC voltage to a − terminal ofthe first comparator 1330. The first DC supply 1320 is connected to aground and the − terminal of the first comparator 1330.

The first comparator 1330 receives a second input voltage through a +terminal, and receives the first DC voltage output by the first DCsupply 1320 through the − terminal. The first comparator 1330 hashysteresis.

That is, the first comparator 1330 outputs a switch control signalhaving hysteresis. The first comparator 1330 changes the switch controlsignal output by the first comparator 1330 to a signal to turn theswitch 13400N when a difference between the second input voltage inputthrough the + terminal and the first DC voltage input through the −terminal is greater than or equal to an ON level. The first comparator1330 changes the switch control signal output by the first comparator1330 to a signal to turn the switch 1340 OFF when the difference betweenthe second input voltage input through the + terminal and the first DCvoltage input through the − terminal is less than or equal to an OFFlevel, which may be less than the ON level to provide a hysteresischaracteristic.

The switch control signal output by the first comparator 1330 may be apulse signal that is synchronized with the first input signal. Theswitch 1340 may be controlled based on the pulse signal. The firstcomparator 1330 having hysteresis may adjust a pulse ON/OFF time.

The switch 1340 is connected to an output of the resistive divider 1310and an input of the amplifier 1350. The switch 1340 is turned ON or OFFbased on the switch control signal, thereby connecting or disconnectingthe resistive divider 1310 and the amplifier 1350.

The amplifier 1350 outputs an amplified voltage by amplifying thedivided voltage output by the resistive divider 1310.

The resistor 1302 of the power device 1020 may have an infinitesimalresistance. A voltage level of a signal output by the switch 1340 may beextremely low. Accordingly, the amplifier 1350 may be provided toamplify the signal.

The second DC supply 1360 outputs a second DC voltage to a − terminal ofthe second comparator 1370. The second DC supply 1360 is connected to aground and the − terminal of the second comparator 1370.

The second comparator 1370 receives as an input, through a + terminal,the amplified voltage output by the amplifier 1350, and receives as aninput, through the − terminal, the second DC voltage. The secondcomparator 1370 has hysteresis. The second comparator 1370 determineswhether the apparatus 1000 or the power device 1020 is to be protectedbased on the amplified voltage output by the amplifier 1350.

That is, the second comparator 1370 outputs a control signal havinghysteresis. The second comparator 1370 changes the control signal outputby the second comparator 1370 to a first control signal when adifference between the amplified voltage input through the + terminaland the second DC voltage input through the − terminal is greater thanor equal to an ON level. The second comparator 1370 changes the controlsignal output by the comparator 1370 to a second control signal when thedifference between the amplified voltage input through the + terminaland the second DC voltage input through the − terminal is less than orequal to an OFF level, which may be less than the ON level to provide ahysteresis characteristic. The first control signal is an OFF signal,and the second control signal is an ON signal.

When a level of a peak current flowing through the power device 1020increases, a level of a peak voltage of the signal amplified by theamplifier 1350 also increases. Accordingly, by setting proper hysteresisreference levels for the second comparator 1370, a level for protectionfrom an overcurrent may be set.

The control unit 1070 the RF input signal received from the RF inputterminal 1002 from being input to the power device 1020 when the controlsignal output by the second comparator 1370 is the first control signal,i.e., the OFF signal.

The overcurrent protecting unit 1050 protects the power device 1020 whenthe power device 1020 is operated at an overcurrent, such as anovercurrent caused by improper matching of wireless-coupled powerdevices.

The overcurrent protecting unit 1050 (1) detects a current flowingthrough the power device 1020 based on an input signal, inputs a dividedinput signal to the amplifier 1350 or blocks the divided input signalfrom being input to the amplifier 1350 by performing switching, (3)amplifies the divided input signal and automatically turns the apparatus10000N and OFF using a control characteristic having hysteresis.

FIG. 14 illustrates an example of the overtemperature protecting unit1060 of FIG. 10. The overtemperature protecting unit 1060 includes afirst inductor 1410, a regulator 1420, a thermistor 1430, and a secondinductor 1440.

A bias voltage is applied to the first terminal 1022 of the power device1020, that is, a gate or a base of the power device 1020. In thisinstance, the lower the bias voltage, the lower an RF power that may beinput to and output from the power device 1020. Accordingly, heatgenerated by the power device 1020 may be reduced, so that a temperatureof the apparatus 1000 or the power device 1020 may be reduced.

One end of the first inductor 1410 is connected to the second terminal1024 of the power device 1020. The other end of the first inductor 1410is connected to an input voltage (V_(in)) input of the regulator 1420.That is, the first inductor 1410 receives a signal from the secondterminal 1024 of the power device 1020, and provides the received signalto the regulator 1420 as V_(in).

The thermistor 1430 is connected to a ground and a reference voltage(V_(ref)) input of the regulator 1420.

The regulator 1420 receives V_(in) from the first inductor 1410, andreceives V_(ref) from the thermistor 1430.

The regulator 1420 may be a low-dropout (LDO) regulator or aswitching-mode regulator, such as a buck regulator, a boost regulator,or a buck-boost regulator.

The bias voltage is supplied by the regulator 1420, and depends on aresistance R of the thermistor.

A resistance of the thermistor 1430 as a temperature of the thermistor1430 changes. Accordingly, using this characteristic of the thermistor1430, the bias voltage may be adjusted based on the temperature. Forexample, If the first terminal 1022 is the gate of the power device1020, the bias voltage may be a voltage of the gate ‘V_(gate). thevoltage of the gate may be a product of a reference current I_(ref) andthe resistance R.

For example, the resistance R of the thermistor 1430 decreases as atemperature T of the thermistor 1430 increases, such that R isproportional to 1/T, i.e., R∝1/T. In this example, by using thethermistor 1430 as a reference resistor of the regulator 1420, forexample, the LDO regulator, a voltage output from the regulator 1420decreases as the temperature increases. Consequently, a power outputfrom the apparatus 1000 or the power device 1020 is reduced as thetemperature increases. Accordingly, the temperature of the apparatus1000 or the power device 1020 decreases.

One end of the second inductor 1440 is connected to an output of theregulator 1420. The other end of the second inductor 1440 is connectedto the first terminal 1022 of the power device 1020. The second inductor1440 receives the bias voltage from the output of the regulator 1420,and applies the bias voltage to the first terminal 1022 of the powerdevice 1024.

Instead of or in addition to controlling the bias voltage of a gate or abase that is the first terminal 1022, by controlling a voltage of adrain or a collector that is the second terminal 1024 by the principledescribed above, an amount of power consumed by the power device 1020may be changed, and a temperature of the power device 1020 may becontrolled based on the change in the amount of power consumed by thepower device 1020.

The overtemperature protecting unit 1060 protects the power device 1020when the power device 1020 is operated at a high temperature, such as ahigh temperature caused by improper matching of wireless-coupled powerdevices.

Information detected by the overvoltage protecting unit 1040, theovercurrent protecting unit 1050, and the overtemperature protectingunit 1060 may be transferred to a main process of the apparatus 1000 ora system. The transferred information may be used for a control andcommunication operation of the apparatus 1000 or the system.

FIG. 15 illustrates an example of an overvoltage protection method. In1510, the first resistive divider 1110 of FIG. 11 outputs a firstdivided voltage by dividing an input voltage.

In 1520, the rectifier 1120 of FIG. 11 outputs a rectified voltage byrectifying the first divided voltage.

In 1530, the second resistive divider 1130 of FIG. 11 outputs a seconddivided voltage by dividing the rectified voltage.

In 1540, the comparator 1150 of FIG. 11 receives the second dividedvoltage as an input through a + terminal, and receives a DC voltage asan input through a − terminal. Also, the comparator 1150 changes acontrol signal output by the comparator 1150 to a first control signalwhen a difference between the second divided voltage input through the +terminal and the DC voltage input through the − terminal is greater thanor equal to an ON level, and changes the control signal output by thecomparator 1150 to a second control signal when the difference betweenthe second divided voltage input through the + terminal and the DCvoltage input through the − terminal is less than or equal to an OFFlevel, which may be less than the ON level to provide a hysteresischaracteristic.

The first resistive divider 1110 is connected to the second terminal1024 of the power device 1020 of FIG. 11.

In 1550, the control unit 1070 of FIG. 11 blocks a signal from beinginput to the power device 1020 when the control signal is the firstcontrol signal, and provides the input signal to the power device 1020when the control signal is the second control signal.

The technical descriptions provided with reference to FIGS. 1 through 14are also applicable to this example, and accordingly will not berepeated here for conciseness.

FIG. 16 illustrates an example of an overcurrent protection method. In1610, the resistive divider 1310 of FIG. 13 outputs a divided voltage bydividing a first input voltage.

In 1620, the first comparator 1330 of FIG. 13 outputs a switch controlsignal. The first comparator 1330 receives a second input voltage as aninput through a + terminal, and receives a first DC voltage as an inputthrough a − terminal.

In 1630, the switch 1340 of FIG. 13 is turned ON or OFF based on theswitch control signal. When the switch 1340 is turned ON or OFF based onthe switch control signal, the resistive divider 1310 and the amplifier1350 of FIG. 13 are connected or disconnected. The first comparator 1330changes a switch control signal to a signal to turn the switch 1340 ONwhen a difference between the second input voltage input through the +terminal and the first DC voltage input through the − terminal isgreater than or equal to an ON level. The first comparator 1330 changesthe switch control signal to a signal to turn the switch 1340 OFF whenthe difference between the second input voltage input through the +terminal and the first DC voltage input through the − terminal is lessthan or equal to an OFF level, which may be less than the ON level toprovide a hysteresis characteristic.

In 1640, the amplifier 1350 outputs an amplified voltage by amplifyingthe divided voltage.

In 1650, the second comparator 1370 of FIG. 13 receives the amplifiedvoltage as an input through a + terminal, and receives a second DCvoltage as an input through a − terminal. The second comparator 1370changes a control signal output by the second comparator 1370 to a firstcontrol signal when a difference between the amplified voltage inputthrough the + terminal and the second DC voltage input through the −terminal is greater than or equal to an level, and changes the controlsignal output by the comparator 1370 to a second control signal when thedifference between the amplified voltage input through the + terminaland the second DC voltage input through the − terminal is less than orequal to an OFF level, which may be less than the ON level to provide ahysteresis characteristic.

The resistive divider 1310 is connected to the second terminal 1024 ofthe power device 1020 of FIG. 11.

In 1660, the control unit 1070 of 11 blocks a signal from being input tothe power device 1020 when the control signal is the first controlsignal, and provides the input signal to the power device 1020 when thecontrol signal is the second control signal.

The technical descriptions provided with reference to FIGS. 1 through 15are also applicable to this example, and accordingly will not berepeated here for conciseness.

FIG. 17 illustrates an example of an overtemperature protection method.In 1710, the first inductor 1410 of FIG. 14 applies a voltage of thesecond terminal 1024 of the power device 1020 of FIG. 14 to the inputvoltage (V_(in)) input of the regulator 1420 of FIG. 14. One end of thefirst inductor 1410 is connected to the second terminal 1024 of thepower device 1020, the other end of the first inductor 1410 to theV_(in) input of the regulator 1420.

The regulator 1420 may be an LDO regulator or a switching-moderegulator.

The thermistor 1430 of FIG. 14 is connected to a ground and thereference voltage (V_(ref)) input of the regulator 1420. A resistance ofthe thermistor 1430 changes bas a temperature of the thermistor 1430changes.

In 1720, the regulator 1420 outputs a bias voltage based on V_(in) andV_(ref).

In 1730, the second inductor 1440 of FIG. 14 applies the bias voltageoutput from the regulator 1420 to the first terminal 1022 of the powerdevice 1020. One end of the second inductor 1440 is connected to anoutput of the regulator 1420, and the other end of the second inductor1440 is connected to the first terminal 1022 of the power device 1020.

FIG. 18 illustrates an example of an electric vehicle charging system.Referring to FIG. 18, an electric vehicle charging system 1800 includesa source system 1810, a source resonator 1820, a target resonator 1830,a target system 1840, and an electric vehicle battery 1850.

The electric vehicle charging system 1800 has a structure similar to thewireless power transmission system of FIG. 1. The source system 1810 andthe source resonator 1820 in the electric vehicle charging system 1800operate as a source device. The target resonator 1830 and the targetsystem 1840 in the electric vehicle charging system 1800 operate as atarget device.

The source system 1810 may include an AC/DC converter, a power detector,a power converter, and a control/communication unit, similar to thesource device 110 of FIG. 1. The target system 1840 may include amatching network, a rectification unit, a DC/DC converter, a switchunit, a charging unit, and a control/communication unit, similar to thetarget device 120 of FIG. 1

The electric vehicle battery 1850 is charged by the target system 1840.

The electric vehicle charging system 1800 may operate at a resonancefrequency in a band of a few kilohertz (kHz) to tens of MHz.

The source system 1810 may generate power equal to or higher than tensof watts based on a type of charging a vehicle, a capacity of theelectric vehicle battery 1850, and a charging state of the electricvehicle battery 1805, and supply the generated power to the targetsystem 1840 to charge the electric vehicle battery 1850.

The source system 1810 may control the source resonator 1820 and thetarget resonator 1830 to be aligned. For example, when the sourceresonator 1820 and the target resonator 1830 are not aligned, thecontrol/communication unit of the source system 1810 may transmit amessage to the target system 1840 to control alignment between thesource resonator 1820 and the target resonator 1830.

For example, when the target resonator 1830 is not located in a positionenabling maximum magnetic coupling, the source resonator 1820 and thetarget resonator 1830 will not be aligned. When a vehicle does not stopaccurately at a charging station, the source system 1810 may detect aposition of the vehicle, and control the source resonator 1820 and thetarget resonator 1830 to be aligned.

The source system 1810 and the target system 1840 may transmit orreceive an ID of a vehicle and may exchange various messages bycommunicating with each other.

The technical descriptions of FIGS. 2 through 17 are also applicable tothe electric vehicle charging system 1800, and accordingly will not berepeated here for conciseness.

The various units, elements, and methods described above may beimplemented using hardware components and/or software components.Software components may be implemented by a processing device, which maybe implemented using one or more general-purpose or special-purposecomputers, such as, for example, a processor, a controller and anarithmetic logic unit, a digital signal processor, a microcomputer, afield programmable array, a programmable logic unit, a microprocessor orany other device capable of responding to and executing instructions ina defined manner. The processing device may run an operating system (OS)and one or more software applications that run on the OS. The processingdevice also may access, store, manipulate, process, and create data inresponse to execution of the software. For purposes of simplicity, thedescription of a processing device is used as singular; however, oneskilled in the art will appreciate that a processing device may includemultiple processing elements and multiple types of processing elements.For example, a processing device may include multiple processors or aprocessor and a controller. In addition, different processingconfigurations are possible, such a parallel processors.

As used herein, a processing device configured to implement a function Aincludes a processor programmed to run specific software. In addition, aprocessing device configured to implement a function A, a function B,and a function C may include configurations, such as, for example, aprocessor configured to implement functions A, B, and C; a firstprocessor configured to implement function A and a second processorconfigured to implement functions B and C; a first processor configuredto implement functions A and B and a second processor configured toimplement function C; a first processor to implement function A, asecond processor configured to implement function B, and a thirdprocessor configured to implement function C; a first processorconfigured to implement functions A, B, C and a second processorconfigured to implement functions A, B, and C, and so on.

The software may include a computer program, a piece of code, aninstruction, or some combination thereof, for independently orcollectively instructing or configuring the processing device to operateas desired. Software and data may be embodied permanently or temporarilyin any type of machine, component, physical or virtual equipment,computer storage medium or device, or in a propagated signal wavecapable of providing instructions or data to or being interpreted by theprocessing device. The software also may be distributed over networkcoupled computer systems so that the software is stored and executed ina distributed fashion.

In particular, the software and data may be stored by one or morenon-transitory computer-readable storage mediums. The non-transitorycomputer-readable storage medium may include any data storage devicethat can store data that can be thereafter read by a computer system orprocessing device. Examples of a non-transitory computer-readablestorage medium include read-only memory (ROM), random-access memory(RAM), CD-ROMs, magnetic tapes, floppy disks, and optical data storagedevices. Also, functional programs, codes, and code segments forimplementing the examples disclosed herein can be easily constructed byprogrammers skilled in the art to which the examples pertain based onthe drawings and their corresponding descriptions as provided herein.

While this disclosure has been particularly shown and described withreference to examples thereof, it will be understood by one of ordinaryskill in the art that various changes in form and details may be made inthese examples without departing from the spirit and scope of the claimsand their equivalents. It should be understood that the examplesdescribed herein should be considered in a descriptive sense only, andnot for purposes of limitation. Descriptions of features or aspects ineach example are to be considered as being applicable to similarfeatures or aspects in other examples. Suitable results may be achievedif the described techniques are performed in a different order and/or ifcomponents in a described system, architecture, device, or circuit arecombined in a different manner and/or replaced or supplemented by othercomponents or their equivalents. Therefore, the scope of the disclosureis defined not by the detailed description of the disclosure, but by theclaims and their equivalents, and all variations within the scope of theclaims and their equivalents are to be construed as being included inthe disclosure.

What is claimed is:
 1. An overvoltage protector comprising: a firstresistive divider configured to divide an input voltage to produce afirst divided voltage; a rectifier configured to rectify the firstdivided voltage to produce a rectified voltage; a second resistivedivider configured to divide the rectified voltage to produce a seconddivided voltage; and a comparator configured to: receive the seconddivided voltage as an input through a positive (+) terminal of thecomparator; receive a direct current (DC) voltage as an input through anegative (−) terminal of the comparator; output a control signal; changethe control signal output by the comparator to a first control signalwhen a difference between the second divided voltage input through the +terminal and the DC voltage input through the − terminal is greater thanor equal to an ON level; and change the control signal output by thecomparator to a second control signal when the difference between thesecond divided voltage input through the + terminal and the DC voltageinput through the − terminal is less than or equal to an OFF level. 2.The overvoltage protector of claim 1, wherein the first resistivedivider comprises: a first resistor connected to an input of the firstresistive divider that receives the input voltage, and an input of therectifier; and a second resistor connected to the first resistor at theconnection to the input of the rectifier, and a ground; and the secondresistive divider comprises: a third resistor connected to an output ofthe rectifier, and the + terminal of the comparator; and a fourthresistor connected to the third resistor at the connection to the +terminal of the comparator, and the ground.
 3. The overvoltage protectorof claim 1, wherein the rectifier comprises: a diode comprising an anodeconnected to the first resistive divider, and a cathode connected to thesecond resistive divider; and a capacitor connected to the cathode and aground.
 4. The overvoltage protector of claim 1, wherein the firstresistive divider is connected to a drain or a collector of a powerdevice protected by the overvoltage protector.
 5. The overvoltageprotector of claim 4, further comprising a control unit configured toblock a signal from being input to the power device when the controlsignal output by the comparator is the first control signal.
 6. Theovervoltage protector of claim 1, wherein the OFF level is less than theON level to provide the comparator with a hysteresis characteristic. 7.An overvoltage protection method comprising: dividing an input voltageto produce a first divided voltage; rectifying the first divided voltageto produce a rectified voltage; dividing the rectified voltage toproduce a second divided voltage; comparing the second divided voltagewith a direct current (DC) voltage; outputting a control signal based ona result of the comparing; changing the control signal to a firstcontrol signal when a difference between the second divided voltage andthe DC voltage is greater than or equal to an ON level; and changing thecontrol signal to a second control signal when the difference betweenthe second divided voltage and the DC voltage is less than or equal toan OFF level.
 8. The overvoltage protection method of claim 7, whereinthe input voltage is a voltage of a drain or a collector of a powerdevice protected by the overvoltage protection method; and theovervoltage protection method further comprises: blocking a signal frombeing input to the power device when the control signal is the firstcontrol signal; and allowing the signal to be input to the power devicewhen the control signal is the second control signal.